A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
neh 4:1WHILE THE ENEMIES SCOFF, NEHEMIAH PRAYS TO GOD, AND CONTINUES THE WORK. (Neh 4:1-6)
when Sanballat heard that we builded the wall, he was wroth--The Samaritan faction showed their bitter animosity to the Jews on discovering the systematic design of refortifying Jerusalem. Their opposition was confined at first to scoffs and insults, in heaping which the governors made themselves conspicuous, and circulated all sorts of disparaging reflections that might increase the feelings of hatred and contempt for them in their own party. The weakness of the Jews in respect of wealth and numbers, the absurdity of their purpose apparently to reconstruct the walls and celebrate the feast of dedication in one day, the idea of raising the walls on their old foundations, as well as using the charred and mouldering debris of the ruins as the materials for the restored buildings, and the hope of such a parapet as they could raise being capable of serving as a fortress of defense--these all afforded fertile subjects of hostile ridicule.
neh 4:3if a fox go up--The foxes were mentioned because they were known to infest in great numbers the ruined and desolate places in the mount and city of Zion (Lam 5:18).
neh 4:4Hear, O our God; for we are despised--The imprecations invoked here may seem harsh, cruel, and vindictive; but it must be remembered that Nehemiah and his friends regarded those Samaritan leaders as enemies to the cause of God and His people, and therefore as deserving to be visited with heavy judgments. The prayer, therefore, is to be considered as emanating from hearts in which neither hatred, revenge, nor any inferior passion, but a pious and patriotic zeal for the glory of God and the success of His cause, held the ascendant sway.
neh 4:6all the wall was joined together unto the half thereof--The whole circuit of the wall had been distributed in sections to various companies of the people, and was completed to the half of the intended height.
neh 4:7HE SETS A WATCH. (Neh. 4:7-23)
But . . . when Sanballat . . . heard that the walls . . . were made up, and . . . the breaches . . . stopped--The rapid progress of the fortifications, despite all their predictions to the contrary, goaded the Samaritans to frenzy. So they, dreading danger from the growing greatness of the Jews, formed a conspiracy to surprise them, demolish their works, and disperse or intimidate the builders. The plot being discovered, Nehemiah adopted the most energetic measures for ensuring the common safety, as well as the uninterrupted building of the walls. Hitherto the governor, for the sake of despatch, had set all his attendants and guards on the work--now half of them were withdrawn to be constantly in arms. The workmen labored with a trowel in one hand and a sword in the other; and as, in so large a circuit, they were far removed from each other, Nehemiah (who was night and day on the spot, and, by his pious exhortations and example, animated the minds of his people) kept a trumpeter by his side, so that, on any intelligence of a surprise being brought to him, an alarm might be immediately sounded, and assistance rendered to the most distant detachment of their brethren. By these vigilant precautions, the counsels of the enemy were defeated, and the work was carried on apace. God, when He has important public work to do, never fails to raise up instruments for accomplishing it, and in the person of Nehemiah, who, to great natural acuteness and energy added fervent piety and heroic devotion, He provided a leader, whose high qualities fitted him for the demands of the crisis. Nehemiah's vigilance anticipated every difficulty, his prudent measures defeated every obstruction, and with astonishing rapidity this Jerusalem was made again "a city fortified."